200910747 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種直流電壓轉換電路。 【先前技術】 目前，直流電壓轉換電路作為驅動電源，已被廣泛應 用於便攜式液晶顯示器中。一般，便攜式液晶顯示器正常 工作需要一穩定之8V直流電壓及一穩定之3.3V直流電 壓。 請參閱圖1，係一先前技術直流電壓轉換電路之示意 圖。該直流電壓轉換電路10包括一電源（1.5V)ll、一升压 式直流电源变换積體電路（Step-up Dc-dc Converter)13、一 第一調壓電路12、一第二調壓電路14、一第一輸出端15 及一第二輸出端16。 該第一調壓電路12用於將該電源11之1.5V直流電壓 轉換為一 8V直流電壓，並經由該第一輸出端15輸出。該 第一調壓電路12包括一低噪音負輸出電荷泵穩壓器121、 一第一反饋支路122及一第一電容123。該第一電容123 與該第一反饋支路122並聯，其一端接地，另一端連接至 該第一輸出端15。該第一反饋支路122包括串聯之一第一 電阻124及一第二電阻125。 該低噪音負輸出電荷泵穩壓器121用於接收該第一反 饋支路122反饋之電壓，並穩定該第一輸出端15之電壓。 該低噪音負輸出電荷泵穩壓器121之型號為MAX853，其 包括一輸入端1210、一第一反饋接收端1211及一負壓輸 200910747 出端1212。該輸入端1210連接至該電源11，該負壓輸出 端1212連接至該第一輸出端15。該第一反饋接收端1211 連接於該第一電阻124與該第二電阻125之間。 該第二調壓電路14用於將該電源11之1.5V直流電壓 轉換為3.3V直流電壓，並經由該第二輸出端16輸出。該 第二調壓電路14包括一電感141、一二極體142、一第二 反饋支路143及一第二電容144。該電源11依序經由該電 感141、該二極體142之陽極（未標號）、陰極（未標號）連接 至該第二輸出端16。該第二電容144與該第二反饋支路143 並聯，其一端接地，另一端連接至該第二輸出端16。該第 二反饋支路143包括串聯之一第三電阻145及一第四電阻 146 ° 該升壓式直流電源變換積體電路13用於接收該第二 反饋支路143反饋之電壓，並穩定該第二輸出端16之電 壓。該升壓式直流電源變換積體電路13之型號為 MAX856，其包括一第二反饋接收端131及一控制輸出端 132。該控制輸出端132連接至該二極體142之陽極，該第 二反饋接收端131連接於該第三電阻145與該第四電阻 146之間。 惟，該直流電壓轉換電路10之第一調壓電路12係藉 由該低噪音負輸出電荷泵穩壓器12達到一 8V之直流電 壓。通常該低噪音負輸出電荷泵穩壓器12之成本較高，因 此該直流電壓轉換電路10之成本較高。 【發明内容】 8 200910747 有4ί於此，提供一種成本較低且 轉換電路實為必需。 _ 、較小之直流電壓 一種直流電壓轉換電路，其包括 端、一第二輸出端、一變壓器、一—上田’、 别出 古周脲〇 第调壓電路、一第- β ' —升压式直流电源变换積體電& 1京、一 電路包括-電晶體、一第一電容及―：電路。該弟-调壓 電容一端接妯ρ 和私合及弟一二極體。該第一 端依序經由該第—二極體之陽極、陰極出二出 晶體之沒極、源極接地。該電源依序經由‘二：及：電 :調屋電路為該第二輸出端提供-第二電； 流电源变换積體電路用於接收該 二==直 並穩定該第二輪出端之帝厭w %出鳊之反饋電壓， 反饋電壓，接收該第—輸出端之 出端之電壓。體之導通或關閉，以穩定該第—輸 種直流電壓轉換電路，其包括一電 源、一第一輪出 第一調壓電路、—第二 路。該第一调壓 二極體。該第— 端。該第一輸出 變壓器 端、—第二輸出端 雷：Γ路压式直流电源变换積體電 包括一電晶體、-第-電容及-第二 該變壓器及該電 該變壓器及該第 式直流电源变换 端、一第一控制 端連接至該第一 地，另一端連接至該第-輸出 曰、序涇由该第一二極體之陽極、陰極、 曰曰體之沒極、源極接地。該電源依序經由 連接至該第二輸出端。該升压 =電路包括一第一反饋端、—第二反饋 端及—第二控制輸出端。該第-反饋 200910747 輸出端。該第二反饋端連接至該第二輸出端。該第一控制 _ 輸出端連接至該電晶體之閘極，用於根據該第一反饋端之 • 電壓，穩定該第一輸出端之電壓。該第二控制輸出端連接 至該第二調壓電路，用於根據該第二反饋端之電壓，穩定 該第二輸出端之電壓。 相較於先前技術，該直流電壓轉換電路僅需一升壓式 直流電源變換積體電路，再配合二調壓電路便可使該二輸 出端達到二電壓，因此該直流電壓轉換電路之成本較低。 【實施方式】 請參閱圖2,係本發明直流電壓轉換電路第一實施方 式之示意圖。該直流電壓轉換電路20包括一電源21、一 變壓器22、一升压式直流电源变换積體電路23、一第一調 壓電路25、一第二調壓電路24、一第一輸出端27及一第 二輸出端26。該變壓器22包括一初級線圈221及一次級 線圈222。該次級線圈222經由該弟一調區電路25為該弟 一輸出端27提供一第一電壓。該電源21經由該初級線圈 221及該第二調壓電路24為該第二輸出端26提供一第二 電壓。 該第一調壓電路25包括一第一二極體251、一第一電 容252、一電晶體254及一第一反饋支路253。該第一輸出 端27依序經由該第一二極體251之陽極（未標號）、陰極（未 標號）、該變壓器22之次級線圈222之異名端（未標號）、 同名端（未標號）及該電晶體254之汲極、源極接地。該第 一電容252與該第一反饋支路253並聯，其一端接地，另 10 200910747 端連接至5玄第一輸出端27。該第一反饋支路Μ〕包括二 串聯之第-電阻256及第二電阻257。 六該第二調壓電路24包括一第二二極體241、一第二電 :=2及—第二反饋支路243。該電源依序經由該變壓 =22之初級線圈221'該第二二極體241 =未標號)連接至該第二輸出端26。該第二電 §第1=饋支路⑷並聯’其—端接地’另—端連接至該 碥26。該第一反饋支路243包括二串聯之第二電 阻244及第四電阻245。 甲％卜之弟—電 輸出=式直編變換積體電路23包括-第-控制 m二制輸出端以1、一第—反饋端⑽ 反饋支路253反饋之電壓。4 接收該第一 第二反饋支路243反饋之電二==用：接收該 接至該電晶體254之閘極（未標號）。工兩出鳊232連 連接至哕第_ 一士挪 下)以弟一控制輸出端231 = 極體241之陽極。該第-反饋端234連接 於㈣-電阻256與該第二電阻257之間 ：接 233連接於該第三電阻⑽與該第四電阻如“ ==直流電源變換積體電路 二 如234之電產，控制該第一控制輸出端232幹出^反饋 低電平’從而控制該電晶體254之 ；出-电平或 直流電源變換積體電路23根據竽第3 "該升壓式 批制兮穿-^ * 系弟—反饋端233之带厭 控制該弟—控制輸出端231輸出之脈衝 之,昼’ 而控制該變壓器22之初級線 儿之占卫比，從 21之儲能時間。該第二〆 11 200910747 制輸出端231輸出之該脈衝訊號具有一初始占空比。 該升壓式直流電源變換積體電路23之型號可為 MAX856，其第一控制輸出端232係該MAX856之LBO接 腳，該第一反饋端234係該MAX856之LBI接腳，該第二 控制輸出端231係該MAX856之LX接腳，該第二反饋端 233係該MAX856之FB接腳。 該電源21可為1.5V之直流電源。該第一輸出端27 之第一電壓可為一8V。該第二輸出端26之第二電壓可為 3.3V。當該二輸出端27、26之二電壓分別為一 8V及3.3V 時，該第一電阻256及該第三電阻244之阻值可為10K歐 姆，該第二電阻257之阻值可為1.87K歐姆，該第四電阻 245之阻值可為6.2K歐姆，第一電容252之容值可為68 微法，該第二電容242之容值可為100微法。 下面以一8V及3.3V為例，說明該直流電壓轉換電路 20之工作原理： 該直流電壓轉換電路20開始工作時，該升壓式直流電 源變換積體電路23之第二控制輸出端231輸出一初始占空 比之脈衝訊號，該脈衝訊號係低電平期間，該第二二極體 241不導通，該電源21與該變壓器22之初級線圈221構 成一迴路，該初級線圈221產生電動勢，同時該變壓器22 之次級線圈222產生感應電動勢。該脈衝訊號係南電平期 間，該第二二極體241導通，該電源21及該變壓器22之 初級線圈221經由該第二二極體241之陽極、陰極為該第 二電容242充電，並為該第二輸出端26提供第二電壓。同 12 200910747 二電屢經由該第二反饋支路243反饋至該升壓式 '電源受換積體電路23之第二反饋端233。 如果該第二電壓小於3.3V，則該 =支:：3反饋至該升壓式直流電源變換積體電= =饋端233後，該升壓式直流電源變換積體電路^ 減小3亥弟二控制輸出端231輸出之脈衝之占空比， 壓益—22之初級線圈221之儲能時間，提高該第二輸 出端26之第二電麼。 ' 如果該第二電壓高於3.3V，則該第二電堡經由該第二 ㈣支路243反饋至該升壓式直流電源變換積體電路: 饋端233後，該升廢式直流電源變換積體電路^ ^ s該第二控制輸出端231輸出之脈衝之占空比，減小該 變，态22之初級線圈221之儲能時間，從而降低該第二輸 出端26之第二電壓。 ’ 另，該直流電壓轉換電路20開始工作時，由於該 輸出端27之第一電壓瞬間為〇v，該〇v之第一電二由 該第一反饋支路253反饋至該升壓式直流電源變換積體電 路23之第一反饋端234,該升壓式直流電源變換積體電路 2#3控制該第一控制輸出端232輸出高電壓，使該電晶體 導通；由於上述該變壓器22之初級線圈221產生電動勢之 同時，該變壓器22之次級線圈222產生有感應電動勢，= 此該次極線圈222經由該電晶體254之汲極、源極為該第 一電容252充電，同時提高該第一輸出端27之第—電°壓。 如果該第一電壓高於一8V，則該第一電壓經由該第一 13 200910747 反饋支路253反饋至該升壓式直流電源變換積體電路23 •之第一反饋端234後，該升壓式直流電源變換積體電路23 . 控制該第一控制輸出端232輸出低電平，該電晶體254不 導通，該變壓器22之次級線圈222不為該第一電容252 充電，同時該第一電容252經由該第一反饋支路253放電， 從而降低該第一輸出端27之第一電壓。 該直流電壓轉換電路20之第二輸出端26之第二電壓 及第一輸出端27之第一電壓並不限於3.3V及一8V，藉由 調整該直流電壓轉換電路20之各電子元件之參數，便可調 節該第二電壓及該第一電壓。 相較於先前技術，該直流電壓轉換電路20之第一調壓 電路25係採用該變壓器22之次級線圈222、該電晶體254 及該第一二極體251將該電源21之1.5V電壓轉換為一8V 直流電壓，取代了先前技術之低噪音負輸出電荷泵穩壓 器，因此該直流電壓轉換電路20之成本較低。 請參閱圖3，係本發明直流電壓轉換電路第二實施方 式之示意圖。該直流電壓轉換電路30與第一實施方式之直 流電壓轉換電路20大致相同，其主要區別之處在於：該直 流電壓轉換電路30進一步包括一第三電容354及一第四電 容353。該第三電容354 —端接地，另一端連接至該第一 輸出端37。該第四電容353 —端接地，另一端連接至該第 二輸出端36。該該第三電容354與第四電容353分別用於 濾除該第一輸出端37之第一電壓與該第二輸出端36之第 二電壓之雜訊干擾。 14 200910747 综上所述，本發明確已符合發明專利之要件，爰依法 ，出專财請。惟，以上所述者僅為本發明之較佳=方 i枯ί發明之範圍並不以上述實施方式為限，舉凡孰悉本 案技藝之人士援依本發明之精神所作了“ 皆應涵蓋於以下申請專利範圍内。、^’ β飾或變化’ 【圖式簡單說明】 圖1係一先前技術直流電壓 圖2係本發明直流電壓轉換、、電路之不意圖。 圖3係本發明直流電壓轉換=路第一實施方式之示意圖。 【主要元件符號說明】 兔略第二實施方式之示音 直流電壓轉換電路J2〇、3〇 變壓器 電源 1 積體電％ 24 26、36 221 231 233 241 243 245 252 254 257 22 23 第一調壓電路 25 第一輸出端 27、37 次級線圈 222 第一控制輸出端 232 第一反饋端 234 第二電容 242 第三電阻 244 第一二極體 251 第一反饋支路 253 第一電阻 256 第四電容 353 升壓式直流電源變換 弟一调壓電路 第二輸出端 初級線圈 第二控制輸出端 第二反饋端 弟——極體 第二反饋支路 第四電阻 第一電容 電晶體 第二電阻 is 200910747 第三電容 354 16200910747 IX. Description of the Invention: [Technical Field of the Invention] The present invention relates to a DC voltage conversion circuit. [Prior Art] At present, a DC voltage conversion circuit has been widely used as a driving power source in portable liquid crystal displays. In general, portable LCD displays require a stable 8V DC voltage and a stable 3.3V DC voltage for proper operation. Referring to Figure 1, there is shown a schematic diagram of a prior art DC voltage conversion circuit. The DC voltage conversion circuit 10 includes a power supply (1.5V) ll, a step-up DC power conversion conversion circuit (Step-up Dc-dc Converter) 13, a first voltage regulation circuit 12, and a second voltage regulation circuit. 14. A first output terminal 15 and a second output terminal 16. The first voltage regulating circuit 12 is configured to convert a 1.5V DC voltage of the power source 11 into an 8V DC voltage and output the first output terminal 15. The first voltage regulating circuit 12 includes a low noise negative output charge pump regulator 121, a first feedback branch 122 and a first capacitor 123. The first capacitor 123 is connected in parallel with the first feedback branch 122, one end of which is grounded, and the other end of which is connected to the first output end 15. The first feedback branch 122 includes a first resistor 124 and a second resistor 125 in series. The low noise negative output charge pump regulator 121 is configured to receive the voltage fed back by the first feedback branch 122 and stabilize the voltage of the first output terminal 15. The low noise negative output charge pump regulator 121 is of the type MAX853 and includes an input terminal 1210, a first feedback receiving terminal 1211 and a negative voltage input 200910747 terminal 1212. The input terminal 1210 is coupled to the power source 11 and the negative voltage output terminal 1212 is coupled to the first output terminal 15. The first feedback receiving end 1211 is connected between the first resistor 124 and the second resistor 125. The second voltage regulating circuit 14 is configured to convert the 1.5V DC voltage of the power source 11 into a 3.3V DC voltage and output the second output terminal 16. The second voltage regulating circuit 14 includes an inductor 141, a diode 142, a second feedback branch 143, and a second capacitor 144. The power source 11 is sequentially connected to the second output terminal 16 via the inductor 141, an anode (not labeled) of the diode 142, and a cathode (not labeled). The second capacitor 144 is connected in parallel with the second feedback branch 143, one end of which is grounded and the other end of which is connected to the second output end 16. The second feedback branch 143 includes a third resistor 145 and a fourth resistor 146 in series. The boost DC power conversion integrated circuit 13 is configured to receive the voltage fed back by the second feedback branch 143 and stabilize the voltage. The voltage at the second output terminal 16. The boost DC power conversion integrated circuit 13 is of the type MAX856 and includes a second feedback receiving end 131 and a control output 132. The control output 132 is connected to the anode of the diode 142, and the second feedback receiving end 131 is connected between the third resistor 145 and the fourth resistor 146. However, the first voltage regulating circuit 12 of the DC voltage converting circuit 10 reaches a DC voltage of 8V by the low noise negative output charge pump regulator 12. Generally, the cost of the low noise negative output charge pump regulator 12 is relatively high, so the cost of the DC voltage conversion circuit 10 is high. SUMMARY OF THE INVENTION 8 200910747 has a low cost and a conversion circuit is necessary. _, a small DC voltage, a DC voltage conversion circuit, including a terminal, a second output terminal, a transformer, a - Ueda', a second phase of the urea cycle regulator circuit, a -β '-liter Press-type DC power conversion integrated body power & 1 Beijing, a circuit includes - a transistor, a first capacitor and -: circuit. The younger-voltage-regulating capacitor is connected to 妯ρ and the private one and the second-pole. The first end sequentially passes through the anode and the cathode of the first diode, and the source is grounded. The power supply sequentially supplies a second power to the second output terminal through the 'two: and: electricity: the tuning circuit; the current power conversion integrated circuit is configured to receive the two == straight and stabilize the second round of the output The feedback voltage, feedback voltage, and the voltage at the output of the first-output terminal are received. The body is turned on or off to stabilize the first-type DC voltage conversion circuit, which includes a power source, a first wheel-out first voltage-regulating circuit, and a second path. The first voltage regulating diode. The first end. The first output transformer end, the second output end lightning: the circuit voltage type DC power conversion integrated body comprises a transistor, a -first capacitor and - the second transformer and the electric transformer and the first type DC power supply The conversion terminal, a first control terminal is connected to the first ground, and the other end is connected to the first output port. The anode is connected to the anode, the cathode, the cathode of the first diode, and the source is grounded. The power supply is sequentially connected to the second output. The boost = circuit includes a first feedback terminal, a second feedback terminal, and a second control output. The first - feedback 200910747 output. The second feedback end is coupled to the second output. The first control_output is connected to the gate of the transistor for stabilizing the voltage of the first output terminal according to the voltage of the first feedback terminal. The second control output is coupled to the second voltage regulating circuit for stabilizing the voltage of the second output terminal according to the voltage of the second feedback terminal. Compared with the prior art, the DC voltage conversion circuit only needs a boosting DC power conversion integrated circuit, and the second voltage regulating circuit can make the two output terminals reach the two voltages, so the cost of the DC voltage conversion circuit is higher. low. [Embodiment] Please refer to Fig. 2, which is a schematic view showing a first embodiment of a DC voltage conversion circuit of the present invention. The DC voltage conversion circuit 20 includes a power source 21, a transformer 22, a boost DC power conversion integrated circuit 23, a first voltage regulator circuit 25, a second voltage regulator circuit 24, a first output terminal 27, and A second output terminal 26. The transformer 22 includes a primary coil 221 and a primary coil 222. The secondary coil 222 provides a first voltage to the output terminal 27 of the younger via the tuned area circuit 25. The power source 21 provides a second voltage to the second output terminal 26 via the primary coil 221 and the second voltage regulating circuit 24. The first voltage regulating circuit 25 includes a first diode 251, a first capacitor 252, a transistor 254, and a first feedback branch 253. The first output end 27 sequentially passes through the anode (not labeled) of the first diode 251, the cathode (not labeled), the different end of the secondary coil 222 of the transformer 22 (not labeled), the same name end (not labeled And the drain and source of the transistor 254 are grounded. The first capacitor 252 is connected in parallel with the first feedback branch 253, one end of which is grounded, and the other 10 200910747 end is connected to the 5th first output terminal 27. The first feedback branch Μ] includes two series-resistors 256 and a second resistor 257. The second voltage regulating circuit 24 includes a second diode 241, a second electric:=2, and a second feedback branch 243. The power source is sequentially connected to the second output terminal 26 via the primary coil 221' of the transformer=22, the second diode 241=not numbered. The second electrical § 1 = feed branch (4) is connected in parallel with its - terminal grounded - the other end is connected to the turn 26 . The first feedback branch 243 includes two second resistors 244 and a fourth resistor 245 connected in series. A % 卜 — 电 电 电 电 电 电 电 电 电 电 电 电 电 电 电 电 电 电 电 电 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 4 Receiving the feedback of the first second feedback branch 243, the second is used to: receive the gate (not labeled) connected to the transistor 254. The two outputs are connected to the 鳊 哕 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ The first feedback terminal 234 is connected between the (four)-resistor 256 and the second resistor 257: the connection 233 is connected to the third resistor (10) and the fourth resistor such as "== DC power conversion integrated circuit 2, such as 234 Production, control the first control output 232 to dry out / feedback low level 'to control the transistor 254; out-level or DC power conversion integrated circuit 23 according to the third " the boost batch兮 wear-^ * The younger brother - the feedback terminal 233 with the anaphoric control of the younger brother - control the output of the output 231 pulse, 昼 ' and control the transformer 22 primary line to occupy the ratio, from 21 energy storage time. The pulse signal outputted by the output terminal 231 of the second 〆11 200910747 has an initial duty ratio. The boosted DC power conversion integrated circuit 23 can be a MAX856 model, and the first control output 232 is the MAX856. The LBO pin, the first feedback terminal 234 is the LBI pin of the MAX856, the second control output 231 is the LX pin of the MAX856, and the second feedback terminal 233 is the FB pin of the MAX856. It can be a 1.5V DC power supply. The first voltage of the first output terminal 27 can be an 8V. The second voltage of the second output terminal 26 can be 3.3 V. When the voltages of the two output terminals 27 and 26 are respectively 8 V and 3.3 V, the resistance values of the first resistor 256 and the third resistor 244 can be For a 10K ohm, the resistance of the second resistor 257 can be 1.87K ohms, the resistance of the fourth resistor 245 can be 6.2K ohms, and the capacitance of the first capacitor 252 can be 68 microfarads. The second capacitor 242 The capacitance value can be 100 microfarads. The following is an example of 8V and 3.3V, which illustrates the working principle of the DC voltage conversion circuit 20: When the DC voltage conversion circuit 20 starts to work, the boosted DC power conversion integrated circuit The second control output terminal 231 of 23 outputs a pulse signal of an initial duty ratio, and the second diode 241 is not turned on during the low period of the pulse signal, and the power source 21 and the primary coil 221 of the transformer 22 form a In the loop, the primary coil 221 generates an electromotive force, and the secondary coil 222 of the transformer 22 generates an induced electromotive force. The second diode 241 is turned on during the south level of the pulse signal, and the power source 21 and the primary coil of the transformer 22 221 via the anode of the second diode 241, The cathode charges the second capacitor 242 and provides a second voltage to the second output terminal 26. The same as 12, 2009, the first power supply is fed back to the boosting power supply converter circuit 23 via the second feedback branch 243. The second feedback terminal 233. If the second voltage is less than 3.3V, the = branch::3 is fed back to the boosted DC power supply to convert the integrated body == the feed terminal 233, the boosted DC power supply product The body circuit ^ reduces the duty cycle of the pulse outputted by the control terminal 231, and the energy storage time of the primary coil 221 of the pressure -22 increases the second power of the second output terminal 26. If the second voltage is higher than 3.3V, the second electric castle is fed back to the boosted DC power conversion integrated circuit via the second (four) branch 243: after the feed end 233, the ascending DC power conversion The integrated circuit ^ ^ s the duty cycle of the pulse outputted by the second control output 231 reduces the energy storage time of the primary coil 221 of the state 22, thereby reducing the second voltage of the second output terminal 26. In addition, when the DC voltage conversion circuit 20 starts to work, since the first voltage of the output terminal 27 is instantaneously 〇v, the first power of the 〇v is fed back to the boosted DC by the first feedback branch 253. a first feedback terminal 234 of the power conversion integrated circuit 23, the boosted DC power conversion integrated circuit 2#3 controls the first control output terminal 232 to output a high voltage to turn on the transistor; While the primary coil 221 generates an electromotive force, the secondary coil 222 of the transformer 22 generates an induced electromotive force, and the secondary coil 222 is charged via the drain of the transistor 254, and the source is substantially charged by the first capacitor 252. The first electrical voltage of an output terminal 27. If the first voltage is higher than one 8V, the first voltage is fed back to the first feedback terminal 234 of the boosting DC power conversion integrated circuit 23 via the first 13 200910747 feedback branch 253. The DC power conversion integrated circuit 23 controls the first control output 232 to output a low level, the transistor 254 is not turned on, the secondary coil 222 of the transformer 22 does not charge the first capacitor 252, and the first The capacitor 252 is discharged via the first feedback branch 253, thereby reducing the first voltage of the first output terminal 27. The second voltage of the second output terminal 26 of the DC voltage conversion circuit 20 and the first voltage of the first output terminal 27 are not limited to 3.3V and 8V, and the parameters of the electronic components of the DC voltage conversion circuit 20 are adjusted. The second voltage and the first voltage can be adjusted. Compared with the prior art, the first voltage regulating circuit 25 of the DC voltage conversion circuit 20 uses the secondary coil 222 of the transformer 22, the transistor 254, and the first diode 251 to apply a voltage of 1.5 V to the power source 21. Converting to an 8V DC voltage replaces the prior art low noise negative output charge pump regulator, so the DC voltage conversion circuit 20 is less expensive. Please refer to FIG. 3, which is a schematic diagram of a second embodiment of the DC voltage conversion circuit of the present invention. The DC voltage conversion circuit 30 is substantially the same as the DC voltage conversion circuit 20 of the first embodiment. The main difference is that the DC voltage conversion circuit 30 further includes a third capacitor 354 and a fourth capacitor 353. The third capacitor 354 is grounded and the other end is connected to the first output terminal 37. The fourth capacitor 353 is grounded at one end and connected to the second output terminal 36 at the other end. The third capacitor 354 and the fourth capacitor 353 are respectively configured to filter out noise interference of the first voltage of the first output terminal 37 and the second voltage of the second output terminal 36. 14 200910747 In summary, the present invention has indeed met the requirements of the invention patent, and is legally required to make a special account. However, the above is only the preferred embodiment of the present invention. The scope of the invention is not limited to the above embodiments, and those skilled in the art will be able to cover the spirit of the present invention. In the scope of the following patent application, ^ 'β decoration or change ' [Simple description of the drawing] Figure 1 is a prior art DC voltage diagram 2 is the DC voltage conversion, circuit is not intended. Figure 3 is the DC voltage of the present invention Conversion = Road Schematic diagram of the first embodiment. [Description of main component symbols] Rabbit's second embodiment of the sound DC voltage conversion circuit J2〇, 3〇 transformer power supply 1 Total electricity 24 24, 36 221 231 233 241 243 245 252 254 257 22 23 first voltage regulating circuit 25 first output terminal 27, 37 secondary coil 222 first control output terminal 232 first feedback terminal 234 second capacitor 242 third resistor 244 first diode 251 first Feedback branch 253 first resistor 256 fourth capacitor 353 boost type DC power converter brother a voltage regulator circuit second output terminal primary coil second control output second feedback terminal brother - polar body second Feeding a first capacitance branch fourth resistor second resistor electrically third crystal capacitor 35416 is 200910747