making 14V programming voltage

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mik3ca

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I just bought a few w77e58 DIP IC's because I needed an 8051 micro with two UARTs. Sadly, this particular chip doesn't have ISP but I'm lucky to still own a parallel port on my computer to make a programmer.

The datasheet for this chip suggests I use 12.5V on VPP for programming voltage and about 14.5V on VPP for erase voltage.

I have a couple thoughts in mind for generating the voltages.

1. Buy power adapter that's 18+V and feed it through 3 voltage regulators in parallel so output of each regulator has 5, 12.5 and 14.5V respectively.

2. Run everything off 5V but somehow make some sort of step-up voltage converter (like a diode/capacitor ladder? would that work)?

I'm trying to think of the best approach here.
 
Around here, retired wall-warts are available at charity thrift shops and yard sales... I have a box full that I keep around for projects...

Do you need all three voltages all of the time?

From what I remember of the older re-programmable micros, you do not need much current at 14.5 or 12.5V, so a simple shunt Zener is good enough.

Maybe a high power 5Vdc source and an ebay step-up converter?
 
I need 5VDC for sure, and I can have either 12.5V or 14.5V along with it. (I don't need 12.5 and 14.5 at the same time)
 
mik3ca said:
The datasheet for this chip suggests I use 12.5V on VPP for programming voltage and about 14.5V on VPP for erase voltage.
Click to expand...

There is usually a VERY TIGHT tolerance on programming voltages including overshoot. On the system I used to program 2716 eproms, it was a linear regulator and a toggle switch. Vpp was off during start-up.
 
I misread it. Its 12V and 14V. So far, I found a voltage doubler made from 555 timer and a few diodes and capacitors, but using that on a 5V source would only give me 10V at best
 
I'm trying to avoid ordering extra pieces online if I can. I mean couldn't I make one from discrete parts I have on hand like diodes, capacitors, transistors and/or op-amps? and that LTC part that was mentioned claims it can do 12V from 5V not 14V.

The parts I have almost immediate access to are also available online at this site: **broken link removed**

As for the rest of the parts, I can see me either paying extreme shipping fees or I wait 21+ days for delivery.
 
Sayal carries LM317s in a TO-92, use one each for 12V and 14V. Start with an un-regulated 16 to 20Vdc wall-wart.

Sayal carries regulated 5Vdc wall-warts...
 
I have a 6VDC wall wart I bought from them. I did make the "Blowit" programmer for the at89C2051 and it uses a resistor network and transistors to switch between 5 and 12V. Could I get away with it if I used 6V, made a voltage tripler then use resistor divider networks from its output to produce 14 and 12V? I tried LM317 regulators in the past and didnt like them.

The blowit programmer details are here: **broken link removed** and the schematic is below.
**broken link removed**
 
LM317 needs very accurate resistors for very accurate voltages. and for the at89c2051 I have 12V and 5V supply for it. What I'd like to do is use just one power supply for this new programmer for the w77e58 IC, so somehow I need a circuit that produces 5, 12, and 14V. and I'll never use the 12 and 14V at the same time.
 
mik3ca said:
LM317 needs very accurate resistors for very accurate voltages....
Click to expand...
so make one or the other variable, as in a pot. I usually set the lower resistor to 100 or 220Ω, then calculate the upper resistor. I choose an upper resistor which is about 10% low, and then make up the difference with a pot...
 
I came up with the following circuit to help with my issue. I'll use an 18V adapter, step it down to 15V then use one regulator to power other circuit parts with dedicated 5V. Then I'll use a simple transistor network shown below to select the voltage I want. Only issue I have is that if no transistor is selected (by making any base a logic high), then the output will be 15V which might destroy the chip since its highest recommended voltage for VPP is 14 for erase operations. I guess I'll have to do alot of number crunching unless theres an easier solution. Heck, ultimately, I want to make the 12v and 14v selections exclusive so I'm wondering if PNP transistors will help here.

 
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