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EPR-21 参数 Datasheet PDF下载

EPR-21图片预览
型号: EPR-21
PDF下载: 下载PDF文件 查看货源
内容描述: 工程原型报告( EP - 21 ) - 30W的DC- DC转换器, DPA424 [Engineering Prototype Report (EP-21) - 30 W DC-DC Converter with DPA424]
分类和应用: 转换器
文件页数/大小: 32 页 / 1244 K
品牌: POWERINT [ Power Integrations ]
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EPR-21 – 5 V, 30 W DC-DC Converter  
19-Nov-02  
4 Circuit Description  
4.1 Primary Circuitry  
The schematic in Figure 2 shows a single-ended forward converter using the DPA424R.  
The circuit is designed for 36 V to 72 V input range and 5 V, 6 A output. C1 and L1  
provide input filtering. C2 and C3 bypass the DC rail. The DC rail is applied to the primary  
winding of T1. The other side of the transformer primary is driven by the integrated  
MOSFET in U1. C8 reduces the amplitude of leakage spikes generated when the  
MOSFET in U1 switches off. VR1 clamps the U1 drain voltage to a safe value during fault  
conditions, but is inactive during normal operation.  
R1 is used to set the low line turn-on threshold to approximately 33 V, and also sets the  
overvoltage shutdown level to approximately 88 V. R3 sets the U1 current limit to  
approximately 85% of its nominal value, limiting the output power delivered during fault  
conditions. C5 bypasses the U1 CONTROL pin, and provides the peak current necessary  
for driving the DPA-Switch internal MOSFET. C6 has three functions. It provides the  
energy required by U1 during startup, sets the auto-restart frequency during fault  
conditions, and also reduces the gain of U1 as a function of frequency. R4 adds a zero  
to stabilize the power supply control loop.  
4.2 Output Rectification  
The output of T1 is rectified and filtered by D2, L2, C10, and C11. This is the lowest cost  
rectification scheme. DPA-Switch is however fully compatible with simple self-driven  
synchronous rectification schemes as described in the DPA-Switch datasheet. C12  
provides additional high frequency filtering, and is located close to the output terminals of  
the supply. C7 provides bypassing for high frequency common-mode noise coupled from  
the primary to the secondary of T1. R14 damps primary-to-secondary circulating current,  
which would otherwise appear imposed on the output ripple voltage.  
C9 and R5 provide some snubbing to D2, but their main purpose is to reset T1 during the  
U1 off time. During the U1 off time, magnetizing energy stored in the T1 primary during  
on time is coupled to the secondary, and charges C9. The voltage on C9 is a 1/2 sinusoid  
with a period determined by C9 and the reflected primary inductance of T1. C9 is sized  
such that the voltage generated during the off time is sufficient to reset T1 before the next  
switching cycle occurs. R5 provides damping for C9 to prevent high frequency ringing  
during switching transitions.  
U1 is powered during normal operation by an auxiliary flyback winding on L2. This  
winding delivers energy during the off time of U1, with an output voltage proportional to  
the supply output voltage. The turns ratio of L2 sets the output voltage of the auxiliary  
winding to approximately 12 V. D1 and C4 rectify and filter the auxiliary winding output.  
Power Integrations, Inc.  
Tel: +1 408 414 9660 Fax: +1 408 414 9760  
Page 6 of 32  
www.powerint.com