• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

replacing L7805 with LM317 linear power regulator;

vari21

Member
Hi again everyone here and happy new year.
I have two willem programmers ,and both have vpp drop issue ,the vpp suppose to be 12.5v but i have only 2.3v on both devices vcc is ok. i made some searchs on internet and i found that the power circuit on willem is terrible, a lot of people complaining of voltage drop problems caused by the 100uh inductor and the step up converter ,so i ve decided to remove the whole circuit L7805, 100uh inductor and the step up converter and replacing them with LM317 or two linear regulators and triming resistors, since the LM317 it s more stable and reliable. my question is that possible ??if it is possible is there any similar shematic ?
thanks in advance
 

wkrug

Active Member
I think the problem is not the 7805, but the step up converter.
Are there 100...220nF Ceramic Capacitators near the Input and Output Pins of the 7805?
The Output Voltage of an 7805 must be lower then the Input Voltage.
To make this shure You can Insert a Diode between Output an Input to avoid this.
( Cathode shows to the Input Side ).
That all will stabilize the 7805.

Do You have a Schematic of that Part.
 

Visitor

Well-Known Member
Load on the Vpp should be next to nothing. If the 7805 is getting hot, you have an excessive current draw somewhere.
 

vari21

Member
the programmer has 4 leds diodes , power led, vcc led ,vpp led the forth i dont know it function it s located near the pic connector.it powers on but the green led number 4 near the pic connector wont light up.
i took a picture from internet to show how my programmer looks like.
 

Attachments

wkrug

Active Member
The Power for the LED 4 was steered By the VCC_ENA Signal.
That comes from the inverting Latch IC12 Y3.
The Output at the end was activated by the INIT Signal on Port A3.

Possible Issues:
Port Y3 don't go down to GND by missing Strobe or Init signal of IC12 ( Volt Meter, Oszilloscope ).
Q3 don't give out the 5V to VCC1, possible no Voltage at the VCC Line.
Something wrong around LED 4.
 

wkrug

Active Member
The INIT Signal is at the Resistor R20 the other side is connected Pin 4 ( A3) at IC 12.
Has RX really 100kOhm ? When there are only 100Ohm it can't work.
I dont know something about the Programmer but I think there is only +5V Signal at the Init Line, that will be Inverted by IC 12.

First I would Check the Signal at Pin 16 ( Y3 ) of IC 12.
There must be a GND Signal when the Init Process is finished.
The Init Signal must be sent via the X1 Connector by an external Unit
 

vari21

Member
Hi wkrung ,i ve checked today the ic 12 with multimeter ,pin16 Y3 030. v
i think i ve fried the m74hc540 ic by plugging something wrong.
excuse me for asking a lot of things ,i ve got another question is it possible to remove the L7805 mc0634 inductor and replace them with X2 LM317 one for vpp ,and the other one for vcc?? i think is possible but im not sure thanks again.
 

Latest threads

EE World Online Articles

Loading
Top