Browse Prior Art Database

Novel Technique to Reduce Bulk Cap Size in a Power Supply with a Boost Converter

IP.com Disclosure Number: IPCOM000019328D
Publication Date: 2003-Sep-11
Document File: 4 page(s) / 367K

Publishing Venue

The IP.com Prior Art Database

Abstract

The novel technique to reduce the value and thus the size of the bulk capacitance in a power supply having a boost front end and has a requirement of definite hold up time, during failure of input power.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 43% of the total text.

BULK CAPACITOR REDUCTION TECHNIQUE

Fig. 1

 
Following description explains the proposed technique to reduce the value and thus the size of the bulk capacitance in a power supply having a boost front end and has a requirement of definite hold up time, during failure of input power.

The circuit shown above in Fig. 1 is the basic configuration of the invention. It shows the front end of an AC to DC power supply having a bridge rectifier, a boost choke L1, boost switch Q1, boost diode D1 and bulk capacitor C3. The other two capacitors C1 and C2 are low value, high frequency de-coupling capacitors. SW1 and SW2 represent switches, which could be a static switch like an Electro-magnetic relay or a semiconductor switch.


The switches SW1 and SW2 are controlled by a control circuit such that, during normal operation, SW1 is closed, thus connecting the bulk capacitor C3, directly across the Bulk + and Bulk - and SW2 is in open state. This is the conventional position of the bulk capacitor. In this normal operation, the circuit configuration looks as shown in Fig.2 below:

Fig. 2

 
Thus the switch SW1 is closed and diode D2 is shunted. The bulk capacitor performs normal filtering and energy storing action just as in a conventional power supply.

Now, when the input AC voltage fails, it is quickly detected by a fast AC fail detect circuit and the control circuit switches SW1 to open position and SW2 to closed position. Now during the AC fail detect circuit delay, the bulk capacitor C3 provides hold up power to the down stream DC to DC converter just like a conventional power supply, as it is placed directly across the Bulk + and Bulk – line. Normally, such DC to DC converter can operate till its duty cycle reaches its maximum permissible limit. For a 400V DC nominal bulk voltage, this limit is normally reached when bulk voltage falls to 300V DC level and then output voltage of the power supply loses regulation.

When the switch contact SW1 has disconnected C3 from its natural position, as shown in Fig.2 but C3 is not yet connected to the proposed position by SW2, C3 still provides power to the DC to DC converter through diode D2 as shown below in Fig. 3:

 
 

Fig. 3

 

Thus the hold-up operation of the DC to DC converter is not affected.

Once the change over operation of the switches is completed, C3 gets effectively connected across C1, at the input of the boost converter. Its new position is shown below in Fig. 4:

 
 

Fig. 4

 
 

Now, the boost converter has capability to switch at very high duty cycle, typically exceeding 95%. Thus it can keep on delivering power to the DC to DC converter and keep the bulk voltage at nominal level across C2, till C3 discharges to a very low level. For a nominal 400V bulk level and for a boost converter designed to operate on a wide range AC supply of 85VAC to 265VAC, such operation can continue till C3 discharges up to 50V DC threshold. Thus most of the energy stored in the bulk capacitor is utilized.

In conventional configuration, the util...